U.S. Pat. No. 5,263,462 discloses a method for checking a tank ventilation device.
The method makes use of the natural formation of a vacuum inside the tank ventilation device when an internal combustion engine is not running. According to the method, after turning off the internal combustion engine, the decrease in the coolant temperature is monitored by a temperature sensor. If the coolant temperature drops below a certain value, a check is made as to whether a pressure switch arranged in the tank ventilation device has closed. The closure of the pressure switch indicates formation of the natural vacuum inside the tank ventilation device, when the pressure switch is closed, one can therefore rule out a leak inside the tank ventilation device.
The disadvantage with this method is that it can only be performed when the internal combustion engine is not running, because the tank ventilation device only cools sufficiently sharply when the internal combustion engine is not running. Sufficient cooling, however, only occurs after a prolonged cooling period, which limits the feasibility of the method to periods in which the engine is off for prolonged intervals. Furthermore, the feasibility of the method also depends on the ambient temperature. If ambient temperatures are too high, the tank ventilation device does not cool sufficiently for the natural vacuum to form. Even when there is sufficient cooling, the amount by which the pressure drops is relatively small, so that the method is prone to errors and requires a large amount of calibration effort.